Submission #16686

#	Time	Username	Problem	Language	Result	Execution time	Memory
16686		suhgyuho_william	Race (IOI11_race)	C++98	0 / 100	9 ms	9720 KiB

race

#include "race.h"
#include <vector>
#include <queue>
#include <algorithm>
using namespace std;
// 문제 : frozen 과 비슷

int i,n,k;
int answer = 999999999;
vector<pair<int,int> > edge[200002];
queue<pair<int,int> > q,qt;
int root[1000002],small[1000002];
bool check[200002],checkv[200002];
vector<int> down[200002];
queue<int> qv;
int downcnt[200002];

int sizes;
void make_down(int v){
    int nextv;

    qv.push(v);
    checkv[v] = true;
    while(!qv.empty()){
        v = qv.front();
        qv.pop();
        sizes = edge[v].size();

        for(i=0; i<sizes; i++){
            nextv = edge[v][i].first;
            if(!checkv[nextv]){
                checkv[nextv] = true;
                qv.push(nextv);
                down[v].push_back(nextv);
            }
        }
    }
}

int find_sum(int x){
    int sum = 1;
    int tmp;

    sizes = down[x].size();
    for(i=0; i<sizes; i++){
        tmp = find_sum(down[x][i]);
        sum += tmp;
    }
    downcnt[x] = (sum-1);
    return sum;
}

int find_middle(int x){
    int nextv;
    int tmp;

    while(1){
        sizes = down[x].size();
        for(i=0; i<sizes; i++){
            nextv = down[x][i];
            if(!check[nextv] && downcnt[nextv]+1 > (downcnt[x]+1)/2) break;
        }

        if(i == sizes) break;
        tmp = downcnt[x]+1;
        downcnt[x] -= (downcnt[nextv]+1);
        downcnt[nextv] += tmp;
        down[nextv].push_back(x);
        x = nextv;
    }

    return x;
}

void dfs(int v,long long sum,int cnt){
    int nextv;

    if(sum > k) return;
    check[v] = true;
    q.push(make_pair(sum,cnt));
    qt.push(make_pair(sum,cnt));

    sizes = edge[v].size();
    for(i=0; i<sizes; i++){
        nextv = edge[v][i].first;
        if(check[nextv]) continue;
        dfs(nextv,sum+edge[v][i].second,cnt+1);
    }
    check[v] = false;
}

// T(n) = 2T(n/2) + O(n);

void race(int x){
    int nextv;
    int tsum,tcnt;
    int v = find_middle(x);

    check[v] = true;
    sizes = edge[v].size();

    root[0] = v;
    small[0] = 0;
    for(i=0; i<sizes; i++){
        nextv = edge[v][i].first;
        if(check[nextv]) continue;
        dfs(nextv,edge[v][i].second,1);

        while(!q.empty()){
            tsum = q.front().first;
            if(root[k-tsum] == v) answer = min(answer,small[k-tsum] + q.front().second);
            q.pop();
        }
        while(!qt.empty()){
            tsum = qt.front().first;
            tcnt = qt.front().second;
            qt.pop();

            if(root[tsum] != v){
                root[tsum] = v;
                small[tsum] = tcnt;
            }else if(small[tsum] > tcnt) small[tsum] = tcnt;
        }
    }

    for(i=0; i<sizes; i++){
        nextv = edge[v][i].first;
        if(!check[nextv]) race(nextv);
    }
}

int best_path(int N, int K, int H[][2], int L[])
{
    n = N; k = K;
    for(i=0; i<n-1; i++){
        edge[H[i][0]].push_back(make_pair(H[i][1],L[i]));
        edge[H[i][1]].push_back(make_pair(H[i][0],L[i]));
    }
    for(i=0; i<=k; i++) root[i] = -1;

    make_down(0);
    find_sum(0);
    race(0);

    if(answer == 999999999) answer = -1;
    return answer;
}

Compilation message (stderr)

race.cpp: In function 'int find_middle(int)':
race.cpp:54:9: warning: 'nextv' may be used uninitialized in this function [-Wmaybe-uninitialized]
     int nextv;
         ^~~~~

• Subtask 1: 0 / 9
• Subtask 2: 0 / 12
• Subtask 3: 0 / 22
• Subtask 4: 0 / 57